Walking away is never easy, and it's natural for sporting figures -- the masters of their domain for so long -- to want to hang on. But when is enough enough? When can you tell?

How do you make the decision?

Three stories in the news today highlight the issue. All deal with names as big as they get in their field -- Joe Paterno, Peyton Manning, Rich Franklin. And all beg those same questions, albeit in very different ways.

That's not to say any of them should walk away today. But the questions are there.

Paterno, 84, has reportedly been told by his doctors to coach Saturday's game against Alabama from the press box. He doesn't want to.

Manning, 35, is dealing with his third neck surgery in 19 months, and will miss at least half of the regular season.

Franklin, 36, is suffering from a torn labrum, and will likewise require surgery and 2-3 months of rehab work.

It's fair to bring up the "R" word in each case -- for three different reasons. The ultimate decisions are theirs alone ... but there's surely some thinking to do in each case.

Paterno's situation is the most obvious. He's simply no longer capable of dealing with the demands of leading a major college football program. His standing on the sideline presents a danger to himself and others, and traveling for recruiting purposes is all but out of the question. Simply put, he's hurting Penn State far more than he's helping it.

But don't tell him that. JoePa's had several golden opportunities to hang 'em up, and he's ignored each one. Would you make the same decision? Would I? We just can't know.

The calculus for Manning is just as perplexing. Surely, he wants his career to continue. He's still one of the top three quarterbacks in the NFL. But neck surgery is a tricky thing, and there's no way of knowing whether he'll ever be the same QB again -- let alone whether he'll be 100 percent safe on the football field.

The last point is the most vexing. It's hard to watch athletes hang on too long, putting their post-retirement quality of life in jeopardy. Manning isn't doing that yet, but the day isn't far off. At what point is it time to simply quit, relax and enjoy untold millions ... and relatively good health?

Franklin's injury, meanwhile, presents no immediate health risks. In the grand scheme -- especially for a mixed martial artist -- a torn labrum is no big deal. Even if he rushed a recovery, he's not running any risk of ruining his life.

No, Franklin should probably start weighing retirement for a more conventional reason: It's getting close to time. By the point he can get back in the ring, he'll be 37 years old. He's alternated losses and wins since dropping a split decision to Dan Henderson at UFC 93, and he's not a real factor in the light heavyweight division. Wrapping it up after another bout or two wouldn't be tragic, like if Manning were forced out of the league. It would just be ... normal.

And that's the thing in sports. Everyone retires. Every circumstance is different, and every decision is tough. None are the same, and none is easy.